[Branch-Rename] Fix some links

According to the [[ https://foundation.llvm.org/docs/branch-rename/ | status of branch rename ]], the master branch of the LLVM repository is removed on 28 Jan 2021.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D95766

GitOrigin-RevId: 94fac81fccfef9917e94bed398781744fb82e159
diff --git a/README.md b/README.md
index 20a0781..7e5352b 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,7 @@
 also review [how flang uses modern C++ features](docs/C++17.md).
 
 If you are interested in writing new documentation, follow 
-[markdown style guide from LLVM](https://github.com/llvm/llvm-project/blob/master/llvm/docs/MarkdownQuickstartTemplate.md).
+[markdown style guide from LLVM](https://github.com/llvm/llvm-project/blob/main/llvm/docs/MarkdownQuickstartTemplate.md).
 
 ## Supported C++ compilers
 
diff --git a/docs/_templates/indexsidebar.html b/docs/_templates/indexsidebar.html
index 3c8f1ab..b6f7942 100644
--- a/docs/_templates/indexsidebar.html
+++ b/docs/_templates/indexsidebar.html
@@ -4,21 +4,21 @@
 <h3>Documentation</h3>
 
 <ul class="want-points">
-    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/README.md#getting-started">Getting Started</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/blob/main/flang/README.md#getting-started">Getting Started</a></li>
 </ul>
 
 <h3>Getting Involved</h3>
 <! TODO: Point links to website(flang.llvm.org) and not github once webpage comes up.>
 <ul class="want-points">
-    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/docs/GettingInvolved.md#mailing-lists">Mailing Lists</a></li>
-    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/docs/GettingInvolved.md#chat">Slack</a></li>
-    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/docs/GettingInvolved.md#calls">Calls</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/blob/main/flang/docs/GettingInvolved.md#mailing-lists">Mailing Lists</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/blob/main/flang/docs/GettingInvolved.md#chat">Slack</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/blob/main/flang/docs/GettingInvolved.md#calls">Calls</a></li>
 </ul>
 
 <h3>Additional Links</h3>
 
 <ul class="want-points">
-    <li><a href="https://github.com/llvm/llvm-project/tree/master/flang/">Github Repository</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/tree/main/flang/">Github Repository</a></li>
     <li><a href="https://bugs.llvm.org/">Bug Reports</a></li>
     <li><a href="https://reviews.llvm.org/">Code Review</a></li>
 <! TODO: Have the bots setup first>
diff --git a/docs/flang-c-style.el b/docs/flang-c-style.el
index 1749b5d..949702a 100644
--- a/docs/flang-c-style.el
+++ b/docs/flang-c-style.el
@@ -9,7 +9,7 @@
 ;; Define a cc-mode style for editing C++ codes in Flang.
 ;;
 ;; Inspired from LLVM style in
-;;    https://github.com/llvm-mirror/llvm/blob/master/utils/emacs/emacs.el
+;;    https://github.com/llvm/llvm-project/blob/main/llvm/utils/emacs/emacs.el
 ;;
 
 (c-add-style "flang"